Magic

People keep coming to me because they want to know how magic works. The truth is, I've got no clue either.

— Archmage Cain Nihil, leader of the Inquisition

Magic is a force that originates in the Spirit Realm. For centuries, every effort has been made to research it, yet even then, knowledge about it is frustratingly scarce. However, the efforts of researchers have borne some fruit.
What, exactly, magic is is still up to debate. It is known, however, that in its natural state, magic only exists in the Spirit Realm. How it interacts with the Spirit Realm is, again, unknown, though it is often theorized that magic is powerless within the Spirit Realm.
Ordinarily, reaching anything from the Spirit Realm is impossible. However, as the races evolved, more advanced races developed something known as a soul shard; a small organ inside the heart. This soul shard serves as something of a transport system between the Spirit World and the paired universes. How it does this is unknown, but what is more important is what it allows those races to do; namely, pull magic from the Spirit Realm down onto Verta or Aead.
Magic, when in one of the paired universes, is speculated to be capable of doing anything. However, it cannot do anything on its own; it must be controlled by someone. Fortunately, possession of a soul shard also allows the creature in question to exert a degree of control over the magic it calls down. This does not mean, however, that creatures with soul shards can do anything.
When utilizing magic, there are two main limitations. The first is power - more potent effects require more magic, yet a soul shard is only so powerful, and can only call down so much magic at a time. The second is control - magic by itself is a very simple substance, and controlling it is hard, especially if one wishes to do something complex.
Both limitations, however, can be mitigated. The power of one's soul shard can be improved through practice, and learning control is simply a matter of training one's mind. Those who manage to power through both limitations can, to at least some degree, use magic to shape the world¹ - they are known as mages.

Manifestation

In most races with soul shards, especially intelligent ones, their soul shard is very weak at birth. Therefore, it requires rigorous training to be able to call down enough magic to cause even the slightest effect. Even once one achieves that, however, their magic will not actually do anything for them until they learn to control it. For these reasons, becoming a mage is very difficult - but in theory, anyone can do it.
Once the art of magic is mastered, it can be used in many ways. As previously stated, magic is capable of doing seemingly anything - the only limitations are the power of the soul shard and how good the mage is at controlling it.
Ways to use magic are divided into four types:

Silver magic

The term "silver magic" refers to something that can be done by a mage using nothing more than an effort of will. For an unknown reason, magic used this way can only be projected from a free hand. Of course, what actually fits in this category depends on the mage, and the precise level of control that mage can achieve. However, in general, silver magic tends to be very simple. Despite its simplicity, however, it can still be powerful, and it is useful when there is no time to set up any sort of rituals. The most commonly used form of silver magic is the creation and manipulation of matter.

Black magic

Black magic refers to an effect which a mage can achieve only with the help of specific rituals. Like silver magic, this definition is, of course, flexible, depending on the mage in question. However, black magic can be far more complex than silver magic, as rituals can allow for a level of control that simple will cannot compete with. It should be noted, though, that rituals cannot make one's magic more powerful - power relies solely on the soul shard.

Emerald magic

Emerald magic, unlike the other forms of magic use, is not the domain of mages, but rather the domain of certain species. Emerald magic refers to a specific magical effect which a particular species has evolved to be able to achieve on an instinctual level. Since emerald magic is controlled by instincts rather than conscious thought, it can be significantly more complex than silver magic, yet not require any rituals. In addition, species with emerald magic are born with stronger soul shards than other species, allowing them to draw the amount of magic required for their emerald magic without too much training. A dragon's ability to breathe fire is an example of emerald magic.

Shadow magic

Shadow magic is, like emerald magic, not the domain of mages. Rather, a member of a race with a soul shard will occasionally be born with a mutated spirit, thus allowing them to perform a single, specific magical effect on an instinctual level. Individuals with shadow magic, known as "shadow mages", are also born with a stronger than usual soul shard, allowing them to call down enough magic to perform their shadow magic without much training. Shadow magic is similar to emerald magic, but on the level of individuals rather than species. However, there is one difference - while emerald magic is controlled by instincts, shadow magic is controlled directly by the spirit. This allows it to be even more complex than emerald magic.

¹This practice is often also called simply "magic", as in "A mage can do magic".